Abstract

Methods and Results: Labor uterine contraction curves are similar among researchers, countries, years and recording methods. Labor
contraction curve were similar to electric oscillations. Regular labor contraction developed by the positive feed-back system composed of
uterus-hypothalamus- hypophysis-oxytocin. Preterm labor should be treated with tocolysis in very early stage.
Conclusion; Regular labor uterine contraction is biological oscillation of pregnant uterus.

Keywords: Labor; Uterus; Contraction, Oscillation, Preterm labor;

Introduction

Uterine contraction curves recorded in regular labor are similar, and
indifferent among researcher, recorded country, year and recording method
(Figure 1). The author intended to clarify the reason of the similarity.

Figure 1: NUterine contraction curves in labor are uniform in different
countries, years and recording methods

Methods

The author compared the curves of typical uterine contraction and electrical
oscillation (Figure 2), where the shape of ultrasound wave in experimental generator was close to the typical labor contraction. Thus, the author studied
mechanism of electrical oscillation. That was positive feed-back system, where
the output signal of an amplifier was fed back to the input of the amplifier,
where the system oscillated waves of fixed frequency determined by the time
constant of the feed-back system (Figure 3). There was amplifying system
in hypothalamus–hypophysis, which excretes oxytocin to intensify uterine
contraction. Positive feed-back loop was the nerve between the uterus and
brain [1-4]. Thus, a positive feed-back loop was formed by uterus–nerve–
hypothalamus–hypophysis–oxytocin, which was excreted into circulation
stimulating uterus, where the contraction signal was conducted whole uterus
through myometrial cell gap junction slowly in 2 minutes, that was the time
constant of uterine contraction (Figure 4).

Figure 2: Uterine contraction is close to electric oscillation

Figure 3: Electric regular waves are oscillated by positive feed-back of
amplifier output to its Input with the frequency determined by the time
constant guided by CR.

Figure 4: The Mechanism to form regular labor contraction

Results

Thus, uterus contracted in less than 2 minutes and interval was the same
repeatedly, until expulsion of fetus and placenta. The contraction is saturated
with high intensity in the oscillation. Oxytocin secretion is useful to secrete
breast milk and promote uterine recovery after the delivery.

Discussion

As preterm regular contraction is strong oscillation in preterm delivery,
common tocolysis tends ineffective to prolong pregnancy, while it will be
effective in early stage of preterm labor before the oscillation. Particularly in
very early stage detected with vaginal scan B-mode or soft cervix detected by
ultrasound [5]. As Braxton-Hicks contraction is transient contraction after
30 gestational weeks, and it is ineffective to deliver fetus, thus, its study will be
useful to treat preterm labor to prolong pregnancy to full-term delivery.

Conclusion

Normal regular labor contraction is a biological oscillation developed by
uterus-brain positive feed-back system. Its study will be useful in the treatment
of preterm delivery.